From: David Howells Permit ptrace to modify a section that's non-shared but is marked unwritable, such as is obtained by mapping the text segment of an ELF-FDPIC executable binary with into a binary that's being ptraced[*]. [*] Under NOMMU conditions ptrace causes read-only MAP_PRIVATE mmaps to become totally private copies because if a private mapping was actually shared then the debugging setting breakpoints in it would potentially crash other processes. This is done by using the VM_MAYWRITE flag rather than the VM_WRITE flag when deciding whether to permit a write. Without this patch a debugger can't set breakpoints in the mapped text sections of executables that are mapped read-only private, even if the mmap() syscall has taken a private copy because PT_PTRACED is set. In addition, VM_MAYREAD is used instead of VM_READ for similar reasons. Signed-off-by: David Howells Signed-off-by: Andrew Morton --- mm/nommu.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff -puN mm/nommu.c~nommu-permit-ptrace-to-ignore-non-prot_write-vmas-in-nommu-mode mm/nommu.c --- a/mm/nommu.c~nommu-permit-ptrace-to-ignore-non-prot_write-vmas-in-nommu-mode +++ a/mm/nommu.c @@ -1258,9 +1258,9 @@ int access_process_vm(struct task_struct len = vma->vm_end - addr; /* only read or write mappings where it is permitted */ - if (write && vma->vm_flags & VM_WRITE) + if (write && vma->vm_flags & VM_MAYWRITE) len -= copy_to_user((void *) addr, buf, len); - else if (!write && vma->vm_flags & VM_READ) + else if (!write && vma->vm_flags & VM_MAYREAD) len -= copy_from_user(buf, (void *) addr, len); else len = 0; _